Chapter 1 of 6 · Fundamentals
Diagnosis & goals
Prenatal diagnosis and therapeutic goals for fetal urinary tract obstruction
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What the experts said
Prenatal diagnosis of fetal urinary tract obstruction requires ultrasound assessment of keyhole sign, bladder thickness, amniotic fluid volume, and fetal sex.
In male fetuses, posterior urethral valves can be diagnosed prenatally and are amenable to fetal intervention.
Fetal urinary tract obstruction causes pulmonary hypoplasia due to anhydramnios, renal insufficiency from obstructive nephropathy creating renal dysplasia, and bladder dysfunction from distended bladder without cycling.
Therapeutic goals for fetal urinary tract obstruction target three organs: lungs (restore amniotic fluid for normal development), kidneys (decompress obstruction), and bladder (restore detrusor cycling contractions).
Fetal renal function assessment is based on bladder tap for fetal urine analysis, ultrasound evaluation of renal parenchyma for cystic dysplasia, and bladder refilling after bladder tap.
Bladder refilling after vesicocentesis demonstrates that the fetus has the ability to make urine.
In severe renal dysplasia where the fetus makes no urine, the only treatment goal is pulmonary survival by replacing amniotic fluid; kidney function cannot be improved.
In moderate or borderline renal dysplasia where kidneys make small amounts of urine, intervention may be too late to save kidney function but can save the lungs and provide option for renal transplant.
In cases with no renal dysplasia where kidneys make plenty of urine, intervention can theoretically save both kidney function and lungs.
Fetal intervention techniques for urinary tract obstruction include percutaneous (bladder aspiration, shunt placement, infusions), fetoscopic (cystoscopy with ureteral catheterization or valve ablation), and open surgery (vesicostomy or cutaneous ureterostomies).
Common vesico-amniotic shunt devices include Rodeck, Harrison, Cook, and Summaex (more commonly used in Europe).
Vesico-amniotic shunt placement has 98% technical success rate but 15% complication rate, with complications carrying 100% mortality due to loss of amniotic fluid.
Overall survival with vesico-amniotic shunting is approximately 50%, and of survivors, 40% will eventually develop end-stage renal disease.
According to Elder et al. 1987, complications of vesico-amniotic shunting include blockage, shunt migration (common as fetuses pull or dislodge the shunt), preterm delivery, urinary ascites, chorioamnionitis, iatrogenic gastroschisis, and abdominal or inguinal herniation.
Open fetal surgery for urinary tract obstruction has limitations including need for deep general anesthesia, maternal laparotomy and hysterotomy, and increased maternal and fetal risk with more prematurity.
Dr. Crombleholme and Dr. Lim at Cincinnati attempted open fetal vesicostomy with minimal uterine exposure, creating a hole in the abdominal wall and marsupializing the bladder for drainage, allowing spontaneous postnatal closure.
In Cincinnati Children's Hospital series, 6 male fetuses at 19-22 weeks gestational age with anhydramnios and normal fetal urine electrolytes underwent open vesicostomy with complete postnatal urinary decompression, no maternal complications, but only 2 of 6 survived.
The main challenge with fetal cystoscopy for posterior urethral valves is the angulation difficulty in visualizing and accessing the posterior urethral valves during surgery.
Cincinnati Children's uses mini-laparotomy approach for fetal cystoscopy with T-fasteners to bring tissue layers together for improved visualization of posterior urethral valves.
In a study by Ruano et al., fetal cystoscopy showed 60% survival compared to 10% in control group.
Transurethral catheter can be placed in combination with laser therapy for posterior urethral valve treatment, using wire to identify and access valves followed by laser ablation and catheter deployment.
According to Ruano et al. 2015 study, fetal cystoscopy had 66% survival, VA shunting had 60% survival, and control group had 17% survival.
Fetal cystoscopy appeared to decrease the incidence of chronic kidney disease in patients with posterior urethral valves in one study.
A 2019 VA study found no difference between VA shunting and fetal cystoscopy regarding chronic kidney disease or survival.
For fetuses with kidney dysplasia and minimal urine output who are not candidates for shunt or cystoscopy, the only option is attempting pulmonary rescue by restoring amniotic fluid from outside.
Methods for restoring amniotic fluid include repeated serial amnio-infusions (initially once weekly, progressing to twice weekly in late gestation) or placement of an amnio-port.
Amnio-port is a metal port used for intravascular medication and parenteral nutrition that can be implanted inside the uterus for easy subcutaneous access for fluid replacement.
In the only published study on amnio-port technique, there were no cases of fetal death related to the procedure, complete restoration of amniotic fluid occurred in all cases, but 6 of 8 fetuses still had pulmonary hypoplasia at birth.
A Birmingham University trial comparing percutaneous shunting to expectant management (15 vs 16 cases) showed a trend toward improved perinatal survival with shunting.
A meta-analysis of 9 papers showed perinatal survival advantage with vesico-amniotic shunt, but 1-2 year survival and renal function outcomes were unclear.
Fetal cystoscopy can be used therapeutically for valve ablation with the goal of fulguration to maintain open urethra.
Cystoscopic ablation of urethral valves with catheterization may improve pulmonary outcomes and possibly renal sequelae and bladder function.
Urethral atresia and cloaca require different management approaches than posterior urethral valves.
Urethrocele can cause bladder obstruction by prolapsing through the posterior urethra, and in females can prolapse completely out due to short urethral distance; treatment options include colon puncture or cystoscopy-assisted laser incision.
Not all cases of fetal urinary tract obstruction require fetal intervention; careful case selection with good diagnosis and multidisciplinary team approach in specialized centers is important.